On January 19, 1984, a Cessna 210D (registration N502RF) was involved in an aviation accident near Rockford, IL. No fatalities were reported. Investigators recorded the probable cause as: The hydraulic system had not been properly bled, allowing entrapped air which resulted in an extremely high flow of air through the secondary relief valve, preventing proper system operation. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a maintenance test flight, the pilot was unable to lower the main landing gear and landed with only the nosewheel down. Post-incident examination found the hydraulic system had not been properly bled, causing entrapped air to disrupt operation.
Incident Overview
A pilot was conducting a maintenance test flight to verify the operation of the landing gear hydraulic power pack. During the flight, the pilot was unable to lower the main landing gear. The aircraft was subsequently landed with only the nosewheel extended.
Investigation Findings
Examination of the hydraulic power pack after the incident revealed that the hydraulic system had not been properly bled. Entrapped air within the system resulted in an extremely high flow of air through the secondary relief valve. This condition prevented the system from operating correctly, which in turn hindered the extension of the main landing gear.
Conclusion
The failure to properly bleed the hydraulic system after maintenance allowed air to become trapped. The presence of air caused an excessively high flow through the secondary relief valve, preventing the landing gear hydraulic system from functioning as intended.
Probable cause
The hydraulic system had not been properly bled, allowing entrapped air which resulted in an extremely high flow of air through the secondary relief valve, preventing proper system operation.
What happened in the 19 Jan 1984 Cessna 210D accident near Rockford, IL?
During a maintenance test flight, the pilot was unable to lower the main landing gear and landed with only the nosewheel down. Post-incident examination found the hydraulic system had not been properly bled, causing entrapped air to disrupt operation.
Were there any fatalities in the 19 Jan 1984 Cessna 210D accident?
No fatalities were recorded in this accident.
What aircraft was involved and where did it happen?
The accident on 19 Jan 1984 involved a Cessna 210D, registration N502RF, at Rockford, IL.
What was the probable cause of the accident?
The hydraulic system had not been properly bled, allowing entrapped air which resulted in an extremely high flow of air through the secondary relief valve, preventing proper system operation.
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